Betting exchange systems have become very popular in recent years. They permit users of client terminals such as personal computers to access a central server over the Internet and place bets on a variety of events. The bets that can be placed are bets either backing an outcome of an event or laying the outcome. For example, in a horse racing event, a user can either back one or more of the horses or can place a single bet laying a particular horse, meaning that he is betting that the horse will not win. Betting exchange systems permit replacement of the traditional bookmaker, so that users are effectively betting against one another.
Online games have also been growing in popularity, with games such as poker widely available over the Internet, and players playing against one another.